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Thread: TBI acting like a carb with maladjusted float.

  1. #1
    Fuel Injected! 1BadAction's Avatar
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    TBI acting like a carb with maladjusted float.

    What would cause this? Driving downhill it acts like the fuel pressure is going up and down. Goes RICH (100BLM) back to 128, then back down, surging. going uphill it just stays at 124-128ish BLM... With roughly 10 gallons in the tank, it idles fine, but then as soon as I fill it up, it's back overly rich again. Could this be because of a bad regulator? Obviously it's impossible to get tuned correctly like this.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  2. #2
    Super Moderator dave w's Avatar
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    One of the challenging things to deal with in tuning are problems like you describe. It's possible the fuel pressure regulator could cause this, but I thinking maybe fuel pump? If I'm understanding what was posted, both uphill / down hill with a full tank of gas have erratic BLM's?

    What I would do, might not affordable or practical for others? I would replace the fuel pressure regulator with a known good fuel pressure regulator. I would "Tee" into the fuel feed supply with a mechanical gauge that I could watch while driving in the conditions that create the problem.

    dave w

  3. #3
    EFI GearHead ! EagleMark's Avatar
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    If you really have this figured out to 10 gallons or half tank versus full tank? I'd say it's not a regulator and probably more a vent, return or CCP issue.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
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  4. #4
    Fuel Injected! 1BadAction's Avatar
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    Yes. Warmed up, half a tank left, drove it around, unplugged computer, plugged computer back in. BLM and INT on the way to the gas station. Put 22 gallons in it to fill it up, BLM at 110 on the way home. Ugh. We'll see how it goes on the way back home tonight and I'll post up.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  5. #5
    EFI GearHead ! EagleMark's Avatar
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    Leave the gas cap loose and see if the issue is still there?

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  6. #6
    Fuel Injected! 1BadAction's Avatar
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    I picked up new injectors and an AFPR pod last week, should have them today. This afternoon I'm going to pick up a fuel cap (It has a locking one on it, junk.) Try that, then if I'm still having issues I may need to drop the tank and inspect the pump/sock/bucket setup. I think it still might be the stock pump, and the fuel filter is unknown also. To top it off I think I have an exhaust leak that has started at the manifold to Y pipe interface which will screw up O2 readings also. ugh.

    It is what it is, just part of getting these things on the road and reliable. At least I have tunerpro so I can see a good bit of what's going on. Otherwise I'd be blind.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  7. #7
    Fuel Injected! devind's Avatar
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    I had the small rubber hose connecter that connects the fuel-pump to the steel line in the tank deteriorate on me once and cause me some gas starvation issues.
    Not really the same symptoms as you are describing but still something to look at.

  8. #8
    Fuel Injected! 1BadAction's Avatar
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    Quote Originally Posted by devind View Post
    I had the small rubber hose connecter that connects the fuel-pump to the steel line in the tank deteriorate on me once and cause me some gas starvation issues.
    Not really the same symptoms as you are describing but still something to look at.
    Great info. It stands to reason that if the rubber section of the return line is doing the same or similar thing, it'll pressurize the return and cause my issues. Makes sense, this is the first time the truck has really been ran since ethanol...

    Truck is back down to half a tank and it's still doing it, on and off. I need to run the rest of the fuel out of it and drop the tank, I guess. That's a crappy job in this 95 degree heat.
    2010 Porsche Cayenne GTS - DD
    1991 2500 Suburban - 454ci BBC tow monster
    1979 16' Action Marine/"Johnny Cash" Merc Bridgeport Champ Motor - Metalflake Maniac

  9. #9
    Fuel Injected! devind's Avatar
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    An easy way to empty the tank is let the fuel pump do the work for you.
    Connect a long piece of fuel hose to the main fuel line then run a jumper on the fuel pump relay and you can pump the fuel out into fuel cans.

    But use caution and keep the fuel far away from the relay just in case you create a spark jumping the relay. Best to have one person man the fuel hose while another mans the relay.

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